Đáp án:
Giải thích các bước giải:
a/ $\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}$
$=\dfrac{2}{3}-\dfrac{60}{175}$
$=\dfrac{2}{3}-\dfrac{12}{35}$
$=\dfrac{2.35}{105}-\dfrac{12.3}{105}$
$=\dfrac{70-36}{105}$
$=\dfrac{34}{105}$
b/ $\dfrac{-2}{5}.\dfrac{5}{8}+\dfrac{5}{8}.\dfrac{3}{5}$
$=\dfrac{-2}{8}+\dfrac{3}{8}$
$=\dfrac{-2+3}{8}$
$=\dfrac{-1}{8}$
c/ $x+\dfrac{1}{2}=\dfrac{3}{4}$
⇒ $x=\dfrac{3}{4}-\dfrac{1}{2}$
⇒ $x=\dfrac{3}{4}-\dfrac{2}{4}$
⇒ $x=\dfrac{3-2}{4}=\dfrac{1}{4}$
d/ $(\dfrac{4}{5}.x+\dfrac{1}{2}).\dfrac{2}{3}=\dfrac{5}{3}$
⇒ $(\dfrac{4}{5}.x+\dfrac{1}{2}=\dfrac{5}{3}:\dfrac{2}{3}$
⇒ $\dfrac{4}{5}.x+\dfrac{1}{2}=\dfrac{5}{3}.\dfrac{3}{2}$
⇒ $\dfrac{4}{5}.x+\dfrac{1}{2}=\dfrac{5}{2}$
⇒ $\dfrac{4}{5}.x=\dfrac{5}{2}-\dfrac{1}{2}=\dfrac{4}{2}=2$
⇒ $x=2:\dfrac{4}{5}=2.\dfrac{5}{4}=\dfrac{5}{2}$
Chúc bạn học tốt !!!
